Method of producing direct positive photographic images



Patented F eb. 21, 195i) METHOD OFPRODUCING DIRECT POSITIVE PHOTQGRAPHIC IMAGES George Earle Fallesen and John Spence, Roch:- ester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application August 13,, 1948, Serial No. 44,215

6 Claims.

This invention relates to photography and particularly to a methodof' making direct positive photographs;

Direct positive efiects may be produced by solarizing the developable latent image by overexposure, by using asecond' exposure-to obtain the Sabbatier orthe Clayden effect or byredeveloping a developed negative image. Solarizable sensitizedproducts require very intense exposures to; obtain: the desired direct positive photograph. The use of a secondexposure has obvious disadvantages from the point of View of practical; technique. Redevelopment adds at least two operations to the usual and: normal. de velopingprocedure.

Falleserr U. S. application Ser.. No; 780,405, filed October: 17; 1947,, describesifcrming a direct positive image inxasuitable: silver halide: emulsion by exposing: the emulsion in the: usual way and developing it in-a developer which; is capableof giving aerial fog; The emulsion'is preferably of the internal latent image type such asvdescribed in Davey and. Knott U. S. patent application Serial No. 790232; filed December 6', 1947, now abandoned.

The Fallesen application Serial No. 780,405 states that certain optical,sensitizing-dyes may; be added to the emulsionlfor the purpose of making it more susceptible toaerialfog. With certain sensitizing dyes While strong absorption of the dye-to-the silver halide'grain. during. exposure is necessary, it is' also desirable that the dye be rapidly removed from the grains inthe processing solutions.

We have found a classof sensitizingdyes which are particularly useful in the process of; the Fallesen application Serial No. 780,405: These dyes are acid merocyanine dyes of the following structure:

X=xygen or sulfur R=carboxymethyl or carboxyphenyl,

'R'=alkyl, e. g ethyl or heptyl,v or phenyl,

and the. benzoxazole nucleus may containtother substituents; such; as; methyl, methoxy, hydit-oxy,

vention.

G=0H-OH= 5 t=s 1 N x N 1- carboxymethyl-5[ (3-ethy1-2 (3) -benzoxazolylidene)- ethylidene] -3-phenyl-2-thiohydantoin omcoorr 1-carboxymethy1-5-[ (3-ethy1-5-methyl-2 (3 -benz0xazolyli dene) -ethylidene] -3-phenyl-2-tl1iohydantoin 01120 O OH CzH5 lcarboxymethyl-5-[ (3-ethyl-5-meth0xy-2 (3) -benzoxazolylidene -ethylidene -3-phenyl-2-thiohydantoin l 0, H2 C O O H Q2115,

lcarboxy-methyl-5- L(31Gthy1-57Ch1OYO'2-(3) -benzoxazolylidene) -ethylidene] -3-phenyl-2-tl1iohydantoin 0 H20 0 O H GQHE l-carboxymethyl-S-E 3-ethyl-5 6-dimethyl-2 (3 .-benz,oxazolylidene) -ethy.lidene '-3'-phenyle2-thiohydantoin 1- -carboxypl1en l-5-[ 3-ethyl-2(3)-benzoxazolylidene)- p ethylidgne]l -phenyl-2-thiol1ydantoin 1-carboxymethyl-5-[ (3-etl1yl2 (3) -benzoxazolylldene) eth eth 1-carboxymethyl-5-[ (3-ethyl-2 (3) -benzoxazolylidene) ethylidene]-3-n-hepty1-2-thiohydantom 1-carboxymethyl-5 (3-ethyl-5carbethoxy-2 (3) -ben zoxazo1- ylidene) -ethylldene -3-pheny1-2-th1ohydanto1n H20 OH 1-carboxymethyl-5 (3-ethyl-5-hydroxy-2 (3) -benzoxazolylidene) -etl1ylide11e] -3-pheny1-2-th10hydanto1n OHaCOOH 1-carboxymethy1-5 (3-ethy1-2 (3) -a-naphthoxa zo1ylidene) ethylidene] -3-phenyl-2-thi0hydanto1n (EH20 0 OH O 2H5 l-carboxymethyl-5-[ (3-ethyl-2 (3) -benzothiaz olylidene) ethylidene]-3-phenyl-2-thiohydant0m 1-carboxymethyl-5-[ (1-ethy1-2 1) -B-naphthothiazolylidene)-ethy1idene]-3-pheny1-2-thiohydantoin 2C=CHCH=C =S a N N 1 1-carboxymethyl-5-[ (3-ethyl-2 (3) -a-naphtl1otl1iazolylidene) -ethy1idene]-3-phenyl-2-1:hiohydantoin The compounds used according to our invention may be made as described in Brooker and Keyes U. S. patent application Serial No. 605,473, filed July 16, 1945, now Patent No. 2,493,748, January 10, 1950.

Compound 1 was made as described in U. S. patent application Serial No. 605,473.

Compound 2 was made by the following method:

1-carboazymethyl-5-[ (Ii-ethyl 5 methyl 2(3) benzoxazolylidene) ethylidene1-3 phenyl 2- thiohydantoin 2.24 g. of 24i-acetanilidovinyl-5-methylbenzoxazole ethiodide (1 mol.), 1.25 g. of l-carboxymethyl-3-phenyl-2-thiohydantoin (1 mol.), 1.01 g. of triethylamine (2 mol.), and 15 cc. ethyl alcohol were refluxed together 15 minutes. The orange reaction mixture was cooled to room temperature, made acid with concentrated hydrogen chloride, and the dye precipitated with water. After cooling to 0 C., the separated dye was filtered off, and washed with water. A yield of 2.1 g. of crude dye was obtained. After twice precipitating from alcoholic triethylamine with concentrated hydrogen chloride, the orange crystals had a M. P. of 216-217" C. with decomposition.

Compound 3 was made similarly to compound 2, using 2-p-acetanilidovinyl-5-methoxybenzoxazole ethiodide instead of the methyl benzoxazole.

Compound 4 was made similarly to compound 2, using 2-5-acetanilidovinyl 5 chlorobenzoxazole ethiodide instead of the methyl benzoxazole.

Compound 5 was made similarly to compound 2, using 2-B-acetanilidovinyl-5,6-dimethylbenzoxazole instead of 5-methylbenzoxazole.

Compound 6 Was made by the following method:

1-p-carbomyphenz/Z-5-H3 ethyl 2(3) benzoacazolylidene) ethylz'dene] 3 phenyl 2 thichydantoin 1.1 g. of 2-fl-acetanilidovinyl-benzoxazole ethiodide (1 mol.), 0.8 g. of 1-carboxypheny1-3- phenyl-Z-thiohydantoin (1 mol.), 0.5 g. of triethylamine (2 mols.), and 10 cc. of absolute ethyl alcohol were refluxed together 30 min. The reaction mixture was cooled to room temperature, made acid with concentrated hydrochloric acid, and cooled to 0 C. The dye was filtered 01f, washed with ethyl alcohol and dried. A yield of 0.6 g. of dye was obtained. After twice precipitating from alcoholic triethylamine with alwens-1c.

coholic hydrogenv chloride, the. brick; redneedleshad M. P... of 313-15. C. withdecomposition.

' QO-NOH; (5112 (I15.

(50011 1warbOmyphenyL3-phenyt 2-thiohydantoin 1.9 g. of 1 carbethoxyphenyl. 3 phenyl 2- thiohydantoin was dissolved in 12' 0.0., of"7' /,5 sodium. hydroxide in water by refluxing for 30 seconds. The. solutionv was chilled in ice. and water. It was made acid with hydrocliloricv acid. The. reaction mixture was chilled to 0C'. It was filtered and washedwellf with water and dried. A yield of 1.5 g. of the freeacid was obtained of M. P. 278-80 with shrinking from. 272".

(llo lTlPh. CH2 CS CI 0 O C2H5 1 -carbethoazyphenyZ'- 3-phenyl-2-thiohydantoin 11.8 g. of carbethoxyphenyl glycine. ethyl: ester (1 mol.) and 6.7 g. of ph'enyl i'sctlsxiocyanate (1 mol.) were heated 36 hours: on asteam bath; The mass was treated with a smalL amount of ethyl alcohol. The solution-was chilledgsthe solid filtered off and washed with a small; amount otethyl alcohol and dried. A yield of 1.9:g'. 188-190" was obtained.

0211500 o O-NHoHzoo.o 02115 33. g. of ethyl-p-aminobenzoate 16.7. g.. of.- ethylbromoacetate and 1100 cc. of ethyl: alcohol were refluxed 48 hrs. The solution-was dissolved in water and the solution made alkaline withsodium carbonate. The product, wasextracted-wlth ether. The ether solution was dried over magnesium sulfate, and the dried-material wasdistilled. A yield. of 11.8 g. of B. P; 240-.25.0/20.-min. was obtained.

Compound '7 was madesimilarlyl to. compound 2, using 2-fi-acetanilidovinylbenzoxazole. ethiodide instead of the methyl derivative; and; 1--ca-rboxymethyl-3-ethyl-2--thiohydantoin (made as fol-- lows) instead of theS-phenylzderivative:

1-carbethoxymethyZ-3-cthyl=2 thiohydantoitz 8.7 g. of ethylisothiocyanate (1 mol.) was added slowly to 18.9 g. of iminodiacetic acid diethylrester (1 mol.) with shaking. Considerable heat was evolved and some alcohol boiled trom-the top of the flask. The mixture washeated. hrs. on, a steam bath, and then. poured into. a beaker. On cooling and stirring. the. material solidified. It was broken. up and usedcrud'e in the preparation. of the free acid. 1 g. of the crude ester was recrystallized from methyl alcohol to give 0.6 of fine white needles 0152M. P. 85-86 C.

1 -oarboxymethyl 3- ethyL-Z thiolwdarttoin 22 g. of 1-carbethoxymethyh3 -ethyl -2 tliiohydantiointl mol.) was: refluxed with-184 cc. of 10% sodium hydroxide until: all wasinv solution. Thesolution was filtered, cooled in ice and water and made acid with concentrated hydrochloric acid. The mixture was chilled to 0 C. and the separated solid was: filtered off, washed well with water anddried; A yield of, 1512 g. of product was obtained of M; P. 160-163 C.

Compound 8 was made similarly to compound 7, using I-carboxymethy1-3-n-heptyl-2 thiohydantoin instead of the 3-ethyl derivative. The 1-carboxymethyl-3-n -heptyl 2i thiohydantoin was made in the same way as they 3-ethyl derivative, starting with n-heptyl isothiocyanate instead of ethylisothiocyanate.

Compound 9 was made similarly to. compound 2, using 2-.,Ci-acetanilidovinyl-4,5-dimethyl-benzoxazole instead of the 5-methylbenzoxazole.

Compound. 10..was.made similarly to compound 2,. using. 2.43-acetanilidovinyl-5-carbethoxy-benzoxazole instead of the 5-methylbenzoxazole.

Com-pound 1 1 was made similarly to compound 2, using- 2-5-acetanilidovinyl-5-hydroxybenzoxazole instead of the- 5-methylbenzoxazole.

Compound 12' was made by the following 7 method:

1,-carbowymethyZ-5-l (3-ethyl. -2 (3).-a-naphthomaeolylidene)ethylidene].-13 -phenyZ-2 thiohydantoin 1 .25. g. of- 1-carboxymethyl-3-phenyl-2-thiohydantoin (1v mol.) 2.4 g. of Z-E-acetanilidovinyla-naphthoxazole ethiodide (1 mol.), 1.35%. of triethylamine (2 mols.) and 15 cc. of absolute ethyl alcohol". were refluxed together for 30 minutes. The orangev solution was. chilled in an iceewater bathaand then: made acid with alcoholic hydrogen chloride (0.1.-g./cc;). Water was added to precipitate. the dye. The mixture was chilled to 0." C., then the separated dye was filtered on and washed with fresh ethyl, alcohol. A yield of 1 g. was obtained; which, after twice being taken up im methyl alcohol with the aid. of triethylamine and precipitating with alcoholic hydrogen chloride, hadiaM'. Prof 232.-3- C,., with decomposition.

- The dye WasQbta-ined as an orange powder.

Compound 13 wasrnade similarly to compound 2, using 2.-,6-acetanilidovinylbenzothiazole ethiodide; instead of the. 5-methylbenzoxazole ethiodide.

Compound 14' was: made by the following methods 1,-carboxymethg Z- 5'-['(1. ethyl 2(1) -B-naphthothiazolylz'dene)rethylidenel -3-phenyZ-2-thiohydantoz'n 5.4 g. of 2-,B-acetanilidovinyl-B-naphthothiazole etho-p-toluene sulfonate (1 mol.), 2.5 g. of l-carlooxymethyl' e 3 phenyl-z thiohydantoin (1 mol.), 2.023%. of triethylamine (2 mol.), and 50 cc. of. ethyl alcohol were refluxed togetherfor 45 minutes. The reaction mixture was cooled to room temperature, and the mixture was made. acid with alcoholic hydrogen chloride (0.1 g./cc.) The mixture wasv chilled to 0 C. and the product filtered ofi and washed with methyl alcohol and water. The dried dye weighed 2 g. After twice precipitating from methyl alcoholic triethylamine with alcoholic hydrogen chloridathe fine maroon crystals had a M. P. of 226-7 C. with decomposition.

Compound 15 was made similarly to compound- 14; using 2 ;9-acetani1idoyinyl-a-naphthothiazole ethoep-toluene. sulfonate instead of the s maphthothiazole.

The photographic emulsion used in the process of our invention is a gelatine silver halide emulsion such as a silver bromide emulsion, a silver bromoiodide emulsion, or a silver chloroiodide emulsion. It need not contain optical sensitizing dyes, although certain sensitizing dyes may be added to it for the purpose of inducing aerial fog, as explained more fully in Fallesen application, Serial No. 780,405. A suitable emulsion is that known as Burtons emulsion, described in Wall, Photographic Emulsions, 1929, pages 52 and 53. Burtons emulsion is made as follows:

A. Silver nitrate grams 100 Water cubic centimeters 500 Ammoniato form clear solution B. Potassium bromide grams 80 Potassium iodide do 50 Soft gelatin do Water cubic centimeters 1,000

C. Dry gelatin "grams" 250 B is heated to 70 C. and A, cold, added to B with constant shaking, digested for 20 minutes at 50 (3., and allowed to cool slowly. C is added after being allowed to swell for 20 minutes in water, drained, and melted. The emulsion is then set and washed.

An internal latent image emulsion, that is, one which forms the latent image mostly inside the silver halide grains, as described on pages 286 and 297 of Mees The Theory of the Photographic Process, 1942, is especially useful for the process of our invention.

Most of the internal latent image emulsions are silver bromo-iodide emulsions of high iodide content, preferably containing at least 10%-20% of iodide. Burtons emulsion is an emulsion of this type, having a silver iodide content of approximately of the content of silver halide. It is not absolutely essential, however, for the emulsion to contain silver iodide.

An internal latent image emulsion made as described in Davey and Knott U. S. application, Serial No. 790,232, filed December 6, 1947, may also be used according to our invention. This emulsion is prepared by first forming in the absence of ammonia and in one or more stages silver salt grains consisting at least partly of a silver salt which is more soluble in water than silver bromide, subsequently converting the grains to silver bromide or silver bromoiodide, and if the silver iodide content of the emulsion is less than 6% calculated on the total silver halide, treating such grains with an iodine compound to bring the silver iodide up to at least 6%, ripening preferably in the absence of ammonia and then either washing out some of the soluble salts or washing out the whole of the soluble salts, followed by the addition of soluble salts such as soluble chloride or bromide. An example of an emulsion made in this way is as follows:

105 grams 0 Water 520 cubic centimeters Solution N0. i:

lEBr 160 grams RI 40 grams at 45 C. l ater 500 cubic centimeters Run solutions Nos. 2 and 3 simultaneously into solution No. 1 in a vessel, taking 90 seconds to do this. Then ripen for 1 minute at 45 C. Next add solution N0. 4 then ripen for 20 minutes at 45 C. Next add 235 grams of inert gelatine (dry). Then ripen at 45 C. for 15 minutes during which time the gelatine dissolves. Set and shred the emulsion and then wash until free from all soluble bromide and then add. about 150 cc. of 10% solution of KCl (by Weight), and then add water to make 3 litres.

An internal latent image type of silver halide emulsion may be defined as one which, when a test portion is exposed to a light intensity scale for a fixed time between and 1 second, and developed for 4 minutes at 20 C. in the ordinary, surface developer (Example 1), exhibits a maximum density not greater than M the maximum density obtained when the same emulsion is equally exposed and developed for 3 minutes at 20 C. in an internal type developer (Example 2). Preferably the maximum density obtained with the surface developer is not greater than the maximum density obtained when the same emulsion is developed in the internal type developer. Stated conversely, an internal latent image emulsion, when developed in an internal" type developer (Example 2) exhibits a maximum density at least 5, and preferably at least 10, times the maximum density obtained when the same emulsion is exposed in the same way and developed in a surface developer (Example 1).

The developer used in the method of our invention should be one which produces oxidation fog or aerial fog. Such developers have been described by Dundon and Crabtree in American Photography, 1924, vol. 18, page 742. An example of such a developer is a hydroquinone developer containing little or no sulfite, and is illustrated in Example 3.

The aerial fog may be produced in the developer in various ways and may be accelerated or intensified by resorting to various expedients. The developer used should preferably have low sulfite ion content and should preferably contain no silver halide solvent more powerful (as a silver halide solvent) than sulfite. Aerial fog may also be increased by bubbling air vigorously through the developer in such manner that the air comes frequently into contact with the emulsion surface of the photograph during development. Certain chemical agents such as copper sulfate incorporated either in the developer or in the emulsion itself may be used to produce or encourage the production of aerial fog. Hydrogen peroxide or certain dyes such as methylene blue increase aerial fog. Fogging agents containing labile sulfur are, however, unsuitable. The fogging action should produce developable surface latent image in the unexposed silver halide grains as explained in the Fallesen patent application Serial No. 780,405.

The acid merocyanine dyes used according to our invention are incorporated in the emulsion before coating in amounts of from 25 to 3000 milligrams of dye per 1000 grams of silver nitrate converted to silver halide. Preferably we use about 375 milligrams of dye per 1000 grams of silver nitrate converted to silver halide.

Our invention is useful both with the aerial fogging developers described in Fallesen application Serial No. 780,405, and also with the developers described in Stauffer U. S. application Serial No. 780,569, new Patent No. 2,497,917, February 21, 1950. The developers of the Stauffer application contain heterocyclic nitrogen containing ring compounds having 5 or 6 atoms in the heterocyclic ring and are so constituted as to increase .themaximum density ofithe positiveimage obtained in developing solutions capable of .producing aerial flog. Typical compounds usedin such developers are benzotriazole, methylbenzo- .triazole, -.nitro-indazole and fiemtro-benzimidazole.

An ordinary surface type developer, that is, one which developsan image only on the surface of the grains of internal latent image emulisions, is the following:

Example 1 pHydroxyphenylglycine grams Sodium carbonate (crystals) "do "100 Water to -liters '1 Development-time, 4 min. 'at 20 C.

An internal type. developer, that is, one which develops "an image inside "the grains of an ".internal latentimage emulsion is the .iollowing:

Example 2 Hydroquinone 'grams '15 Monomethyl p aminophenol sulfate do Sodium sulfite (anhydrous) 'do 50 Potassium'brom'ide do 10 Sodium hydroxide do 25 sodium thiosulfate (crystals) do Water to liters 1 Development time, 3 min. at 20 C.

Our invention will now be described by reference to the following specific examples.

Example .3

To an emulsion suchias the Davey and 'Knott emulsion described above there was added 375 milligrams ,per 1000 grams of silver nitrate .of 1 carboXymeth'yl-5-l (3-ethyl-'2.(f3) -benzoxazoly- 'lidene) ethylidenel 3 -phenyl-Z-thiohydantoin and the emulsion was coated on a support and dried:. It was exposed in an Eastman IIB Sensitometer '(Journal Society Motion Picture Engineers, 17, 1931, page 536) and was then developed for four minutes at "68 'F. in thefollowing developing solution.

Hydroquinone grams 10 Sodium sulfite do 16 Par-aformaldehyde do 4 Sodium carbonate -do l ll iethylbenzotriazole -do 0.4 Water to "liters" l Sensitometric curves were obtained from this exposure and from an identically made and;processed emulsion without the merocyanine rdye. The effect of the dye in increasing the "gamma and maximum densityof the developed image is shown in the following table.

Max. Density Emulsion without. dye Emulsion with dye 7 Example 4 An emulsion made as described .in Example 3 was exposed and developed'inthe same developer as that used'inExampleBbut with a development time of two minutes. "When compared with an identical emulsion .not cOntainingthe merooyanine dye, the resulting image "showed increased contrast and maximum density.

'Ercample 5 An emulsion made as describedinExample 3 was exposed on an Eastman 'IIB Sensitometerand 'Was'then developedior 12 minutes at 68 'F. 'in the following developingsolution.

Hydroquinone grams 22.5 Sodium-sulfite -do 3O .Baraformaldehyde do '75 :Potassium :metabisulfite -'do 26 Boric acid crystals do 7.5 Potassium bromide do 1.6 Water. to 1iters .1

The "developer -'was agitated during thedevelopment by forcing air through-a sintered glass bubble tube completely submerged in the developer tank. .A similar emulsion not containing the merocyan'ine dye was exposed 'in'the same way and developed for the same'length of time 'in the same solution and under the same conditions. The emulsion containing the merocyan'ine ,dye showed increased gamma and maximum density when compared with the emulsion not containing the merocyanine dye.

kit will be understood that the :compoundsand examples included herein are illustrative only and that the appended claims :are torbe taken as a -measure 'of the invention.

We claim:

1. The method of obtaining a direct positive image in- 'a-silver halide emulsion lawer, which comprises exposing to light rays to which the emulsion is sensitive, -a silver halide emulsion layer containing an "acid "dye having the general iormula:

in 'which' X is selected from the class consisting of oxygen and sulfur, R is selected from the class' consisting of earboxymethyl and carboxyphenyl, IR is selected from the class consisting cramp and phenyh'and at least one of the free positions of the azole nucleus contains asubstitu- -ent selected "from the class consisting of hydrogen, methyl, methoxy, hydroxy, chloro, carbethoxy, fused-on benzene rin in the 4,5-position, and fused-on benzene ring in the 6,7-position, a testportionof which-layer uponexposure to a light intensity scale for a fixed time between -and 1 second anddevelopment for 3 minutes 'at 20 0., in'thefol-lowinginternaltype developer:

:I-Iydroquinone "grams" '15 rMonomethyl-p-aminophenol sulfate do '15 Sodium sulfite (anhydrous) do 50 Potassium bromide do 10 ---Sodium hydroxide do .25 Sodium thiosulfate .(cryst'als) do.. '20 Water to liters..- 1 Developmentitime, 3min. at 20 C.

gives a maximum density at least 5 times the maximum density obtained when the equally .exposed "silver halide emulsion is developed for 4 l'niinutes :at 20 'C. in "the following surface developer:

p-Hydroxyphenylglycine grams 10 Sodium carbonate .(crystals) do 100 Water.to liters 1 Development time, 4 min. at 20 'C. and developing the unexposed portion of said ii emulsion layer in" a developing solution which produces aerial fog.

2. The method of obtaining a direct positive image in a silver halide emulsion layer, which comprises exposing to light rays to which the emulsion is sensitive, a silver halide emulsion layer containing .a -[(3-ethyl-2(3) -benzoxazolylidene)-ethylidene]-2-thiohydantoin dye having a carboxymethyl group in the 1-position of the thiohydantoin ring, and an alkyl group in the 3-position of the thiohydantoin ring, a test portion of which layer upon exposure to a light intensity scale for a fixed time between /100 and 1 second and development for 3 minutes at 20 C. in the following interval type developer:

Hydroquinone grams 15 Monomethyl-p-aminophenol sulfate do 15 Sodium sulfite (anhydrous) do 50 Potassium bromide do Sodium hydroxide do 25 Sodium thiosulfate (crystals) do 20 Water to liters 1 Development time, 3 min. at 20 C.

gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emulsion is developed for 4 minutes at 20 C in the following surface developer:

p-Hydroxyphenylglycine grams 10 Sodium carbonate (crystals) do 100 Water to liters 1 Development time, 4 min. at 20 C.

and developing the unexposed portion of said emulsion layer in a developing solution which produces aerial fog.

3. The method of obtaining a direct positive image in a silver halide emulsion layer, which comprises exposing to light rays to which the emulsion is sensitive, a silver halide emulsion layer containing a 5-[(3-ethyl-2(3)-benzoxazolylidene)-ethylidenel-2-thiohydantoin dye having a carboxymethyl group in the l-position of the thiohydantoin ring, and a phenyl group in the 3-position of the thiohydantoin ring, a test portion of which layer upon exposure to light intensity scale for a fixed time between /100 and 1 second and development for 3 minutes at 20 C. in the following internal type developer:

Hydroquinone -1 grams Monomethyl-p-aminophenol sulfate do 15 Sodium sulfite (anhydrous) do 50 Potassium bromide do 10 Sodium hydroxide do 25 Sodium thiosulfate (crystals) do Water to liters 1 Developed time, 3 min. at 20 C.

gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emulsion-is developed for 4 minutes at 20 C. in the following surface developer:

p-I-Iydroxyphenylglycine grams 10 Sodium carbonate (crystals) do 100 Water to liters 1 Development time, 4 min. at 20 C.

and developing the unexposed portion of said emulsion layer in a developing solution which produces aerial fog.

4. The method of obtaining a direct positive image in a silver halide emulsion layer, which comprises exposing to light rays to which the emulsion is sensitive, a silver halide emulsion layer containing a 5-[(3-ethyl-2(3)-benzoxazolylidene)-ethylidene]-2 thiohydantoin dye having a carboxyphenyl group in the 1-position of the thiohydantoin ring, and a phenyl group in the 3-position of the thiohydantoin ring, a test portion of which layer upon exposure to a light intensity scale for a fixed time between and 1 second and development for 3 minutes at 20 C. in the following internal type developer:

Hydroquinone grams 15 Monomethyl-p-aminophenol sulfate do 15 Sodium sulfite (anhydrous) do 50 Potassium bromide do 10 Sodium hydroxide do 25 Sodium thiosulfate (crystals) do 20 Water to liters 1 Development time, 3 min. at 20 C.

gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emulsion is developed for 4 minutes at 20 C. in the following surface developer:

p-Hydroxyphenylglycine grams 10 Sodium carbonate (crystals) do 100 Water to liter 1 Development time, 4 min. at 20 C.

and developing the unexposed portion of said emulsion layer in a developing solution which produces aerial fog,

5. The method of obtaining a direct positive image in a silver halide emulsion layer, which comprises exposing to light rays to which the emulsion is sensitive, a silver halide emulsion layer containing an acid dye having the general formula:

as. i

in which X is selected from the class consisting of oxygen and sulfur, R is selected from the class consisting of carboxymethyl and carboxyphenyl, R. is selected from the class consisting of alkyl and phenyl, and at least one of the free positions of the azole nucleus contains a substituent selected from the class consisting of hydrogen, methyl, methoxy, hydroxy, chloro, carbethoxy, fused-on benzene ring in the 4,5-position, and fused-on benzene ring in the 6,7 -position, a test portion of which layer upon exposure to a light intensity scale for a fixed time between /100 and 1 second and development for 3 minutes at 20 C., in the following internal type developer:

Development time, 3 min. at 20 C.

gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emulsion is developed for 4 13 minutes at 20 C., in the following surface developer:

p-Hydroxyphenylglycine grams" 10 Sodium carbonate (crystals) do 100 Water to 1iters 1 Development time, 4 min. at 20 C.

and developing the unexposed portion of said emulsion layer in a developing solution which produces aerial fog, and containing a heterocyclic, nitrogen-containing ring compound having at least 5 but not more than 6 atoms in the heterocyclic ring.

6. The method of obtaining a direct positive image in a silver halide emulsion layer, which comprises exposing to light rays to which the emulsion is sensitive, a silver halide emulsion layer containing an acid merocyanine dye having the general formula:

X O=O N-R {2\ 1 l4 3i 5 2C=CH-CH= 5 1 2 =s i C2H5 in which R is selected from the class consisting of -carboxymethy1 and carboxyphenyl, R is selected from the class consisting of alkyl and phenyl, and at least one of the free positions of the benzoxazole nucleus contains a substituent selected from the class consisting of hydrogen, methyl, methoxy, hydroxy, chloro, carbethoxy,

fused-on benzene ring in the 4,5 position, and fused-on benzene ring in the 6,7 position, a test portion of which layer upon exposure to a light intensity scale for a fixed time between /100 and 1 second and development for 3 minutes at 20 C in the following internal type developer:

Hydroquinone grams 15 Monomethyl-p-aminophenol sulfate do 15 Sodium sulfite (anhydrous) do Potassium bromide do 10 Sodium hydroxide do 25 Sodium thiosulfate (crystals) do 20 Water to liters 1 Development time, 3 min. at 20 C.

gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emulsion is developed for 4 minutes at 20 C. in the following surface developer:

p-Hydroxyphenylglycine grams 10 Sodium carbonate (crystals) do Water to liters 1 Development time, 4 min. at 20 C.

and developing the unexposed portion of said emulsion layer in a developing solution which produces aerial fog, and containing benzotriazole.

GEORGE EARLE FAILESEN. JOHN SPENCE.

No references cited. 

1. THE METHOD OF OBTAINING A DIRECT POSITIVE IMAGE IN A SILVER HALIDE EMULSION LAYER, WHICH COMPRISES EXPOSING TO LIGHT RAYS TO WHICH THE EMULSION IS SENSITIVE, A SILVER HALIDE EMULSION LAYER CONTAINING AN ACID DYE HAVING THE GENERAL FORMULA: 